1. Field of the Invention
The present invention relates to a data recording apparatus for a vehicle.
2. Description of Related Art
Recently, there has been studied a data recording apparatus for a vehicle (driving recorder) that a recording apparatus referred to as a flight recorder provided in an aircraft or the like is applied to a vehicle. Such a data recording apparatus for a vehicle is configured to constantly record data regarding a traveling state of a vehicle detected by a sensor disposed in the vehicle, and objectively analyzes the factor of emergency state of the vehicle from the recorded data in the post analysis, when the vehicle reaches the emergency state which receives impulsive force of a predetermined value or more from the external, for example (hereinbelow referred to as time of occurrence of event). In such a data recording apparatus for a vehicle, it is not practical to record data of total traveling time because it requires enormous recording capacity, so data of sensor of limited time are recorded by rewriting in a rewritable recording device, and the data of limited time before the time of occurrence of the event are stored to be usable during the post analysis (reference to JP H07-244064A). In addition, the present inventor has been proposed a data recording apparatus for a vehicle capable of recording data of limited time after the time of occurrence of the event (reference to JP 2005-229587).
By the way, for the above data recording devices, generally, output signals of a plurality of sensors such as an acceleration sensor and a vehicle speed sensor, which detects impulsive force applied externally to a vehicle, are often recorded at the same sampling interval. In this case, the sampling interval is set to the fastest sampling interval in sampling intervals required for reproducing each of the output signals based on the frequency range of output signal of each of the sensors. For example, the frequency range of output signal of the acceleration sensor has higher frequency element than the frequency range of the output signal of the vehicle speed sensor, and requires a fast sampling interval. However, if the sampling interval is set as just described, a sensor capable of reproducing an output signal at the sampling interval which is not over the set sampling interval obtains excessive data, resulting in increase in recording capacity and causing rise in costs. In addition, a load on CPU is increased by conducting unnecessary sampling and a high-speed CPU is required, also resulting in rise in costs.
Moreover, it is not always true that the time of occurrence of the event corresponds with the sampling timing. If the time differences between the time of occurrence of the event and the sampling timing are not known in the post analysis, highly accurate analysis can not be performed.